Abstract
With obesity having doubled in the last decade, hypertension is on the rise. In one-third of hypertensive patients the metabolic syndrome is present. This might be one factor for the increasing number of prescriptions for angiotensin receptor blockers and calcium-channel blockers besides a more favorable risk-to-benefit ratio. The aim of the present study was to evaluate a therapeutic drug monitoring (TDM) method for assessment of adherence based on cut-offs in inpatients and to compare it to an established urine drug screening in outpatients. A method for quantification of calcium-channel blockers and angiotensin receptor blockers using high-performance liquid chromatography-tandem mass spectrometric analysis (LC-MS/MS) was developed and validated. The method was applied to serum samples of 32 patients under supervised medication to establish cut-off values for adherence assessment based on dose-related concentrations (DRC, calculated from pharmacokinetic data). Furthermore, corresponding urine and blood samples of 42 outpatients without supervised medication were analysed and the results compared with regard to adherence assessment. All serum concentrations measured for amlodipine (n = 40), lercanidipine (n = 14), candesartan (n = 10), telmisartan (n = 4) and valsartan (n = 10) in inpatients were above the patient specific lower DRC confirming adherence. Of 42 outpatients the identification of analytes in urine as well as the quantification in serum exhibited differing results. According to urinalysis, adherence was demonstrated in only 87.0% of prescriptions, compared to 91.3% for serum analyses. Differences were observed for amlodipine, lercanidipine and candesartan which can be explained by a higher specificity of the serum analysis approach due to pharmacokinetics. The present study confirms that assessing adherence based on serum drug concentrations with individually calculated lower DRCs is more accurate than using qualitative urine analysis. In particular, drugs with low bioavailability, low renal excretion or high metabolism rate such as lercanidipine and candesartan may lead to underestimation of adherence via urine analysis.
Highlights
Hypertension is a widespread disease with a steadily increasing prevalence [1]
The previously described method for quantification of β-blockers and diuretics was extended by five angiotensin receptor blockers (ARBs) and calcium-channel blockers (CCBs)
Since the analyses only looked at ARBs and CCBs, adherence rates referring to individual patients should not be taken as representative for adherence to all drugs of the medication regimen
Summary
Hypertension is a widespread disease with a steadily increasing prevalence [1]. Since high blood pressure is one of the main causes of cardiovascular morbidity and mortality, the prevention and control of hypertension through lifestyle changes [1] and drug therapy is essential [2,3]. Despite the availability of efficient and generally well tolerated antihypertensive drugs, hypertension remains poorly controlled in a substantial proportion, if not the majority of hypertensive patients [4,5]. In a minority of patients, blood pressure remains uncontrolled despite prescription of three or more antihypertensive drug classes–so called resistant hypertension. It is generally accepted that one of the main factors leading to poor blood pressure control and apparent treatment-resistant hypertension (aTRH) is poor drug adherence [6]. This may be explained by the fact that high blood pressure causes few symptoms, especially in its initial stages, while the drugs have unpleasant adverse effects.
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